Monitoring photosensitizer concentration by use of a fiber-optic probe with a small source-detector separation

We present a noninvasive method to track the concentration of photodynamic therapy drugs in real time. The method is based on measurements of backscat tered and fluorescent light with a steady-state fluorescence spectrometer. The ratio of the fluorescent light to the scattered light is found to be li nearly proportional to the absorption coefficient of the photosensitizer. T he fiber-optic probe used for the measurements has a small source-detector separation; therefore the measurements could be performed through the worki ng channel of an endoscope. (C) 2000 Optical Society of America OCIS codes: 170.3890, 170.5180.